Gridded electron tube employing cooled ceramic insulator for mounting control grid

ABSTRACT

The gridded gun of an electron tube includes an annular high voltage beryllia insulator body having good thermal conductivity. The thermionic cathode emitter is mounted within the central bore in the annular beryllia insulator in thermally insulative relation relative to the insulator body. The control grid and focus electrode for the gun are mounted from the surface of the annular insulator facing the anode. The outer periphery of the annular insulator is mounted to the body of the electron tube in heat exchanging relation therewith, such that the control grid is cooled by thermal conduction through the beryllia insulator body to the cooled main body of the electron tube.

United States Patent [191 Miram et a1.

[11-] 3,809,939 [451 May 7,1974

[ GRIDDED ELECTRON TUBE EMPLOYING COOLED CERAMIC INSULATOR FOR MOUNTINGCONTROL GRID [75] Inventors: George V. Miram, Daly City;

Yosuke M. Mizuhara, San Francisco, bothof Calif.

[73] Assignee: Varian Associates, Palo Alto, Calif. [22] Filed: Nov. 8,1972 21 Appl. No.: 304,703

52 us. Cl 313/39, 313/23, 313/46, 313/289 51 Int. Cl. H0lj 1/02 [58]Field of Search 313/19, 23, 28, 39, 46, 1

[56] References Cited UNITED STATES PATENTS 3,706,002 12/1972 Miram etal. 315/539 3,390,292 6/1968 Perugini BER'YLLIA -d Aine; Robert 1gStoddard 5/1972 Jackson 313/39 Primary Examiner-James W. LawrenceAssistant Examiner-Wm. H. Punter Attorney, Agent, or F irm-Stanley Z.Cole; Harry E.

[57] ABSTRACT The gridded gun of an electron tube includes an annularhigh voltage beryllia insulator body having good thermal conductivity.The thermionic cathode emitter is mounted within the central'bore in theannular be= ryllia insulator in thermally insulative relation relativeto the insulator body. The control grid and focus electrode for the gunare mounted from the surface of the annular insulator facing the anode.The outer periphcry of the annular insulator is mounted to the body ofthe electron tube in heat exchanging relation therewith, such that thecontrol grid is cooled by thermal conduction through the berylliainsulator body to the cooled main body of the electron tube.

8 Claims, 3 Drawing Figures GRIDDED ELECTRON TUBE EMPLOYING COOLEDCERAMIC INSULATOR FOR -MOUNTING CONTROL GRID BACKGROUND OF THE INVENTIONfocus electrode were mounted to the beryllia ceramic body, whereas thecathode emitter was mounted in thermally insulative relation relative tothe control grid and relative to the beryllia insulator body. However,both the focus and controlgrid structures as well as the cathode emitterwere mounted well above the surface of the insulator body facing theanode such that a relatively long thermal path was provided between thecon trol grid and the insulator body. This resulted in relatively poorcooling of the control grid through the insulator body to the body ofthe tube.

Cooling of the prior control grid was achieved by placing a fluidcoolant in heat exchanging relation with the grid support structure andhigh voltage insulator body to affect cooling of the control grid. Sucha prior art tube is disclosed and claimed in copending US. Pat.

No. 3,706,002 issued Dec. 12, 1972 and assigned to the same assignee asthe present invention.

While fluid cooling of the control grid support structure and highvoltage insulator assembly results in sufficientcooling for the controlgrid to prevent unwanted thermionic. emission from the control grid whenthe tube is supposedly turned off, it results in an undue complicationof the electron gun assembly. More particularly, the electron gunassembly must include means for containin the fluid coolant or forflowing the coolant through the electron gun in heat exchangingrelationwith the grid support structure. In addition, it

causes the electron gun assembly to be longer than normal due to theadded length caused by the coolant chamber and the baffle structure fordirecting the coolant through the electron gun assembly.

Cooling of the control grid of the electron gun is extremely importantfor if the grid is not sufficiently cooled it will serve as a thermioniccathode emitter when the grid is pulsed negative relative to the cathodefor turning off the tube. This unwanted grid emission can produceinterpulse noise which is highly undesirable in high power pulsedklystron tubes. In a typical example, the cathode emitter may beoperating at 800 C, whereas the control grid should preferably beoperated at a temperaturenot in excess of 200 C. The control grid maybedisposed only 0.039 inches from the hot cathode emitter. Thus very amplecooling for the grid must be provided in orderto maintain at least a 600C differential between the closely spaced control grid and thethermionic cathode emitter. The problem is even further complicated whenthe electron gun assembly is encased in a silicone rubber pottingmaterial for improved electrical insulation at reduced atmosphericpressure, as encountered at high altitudes for airborne applications.The silicone rubber utilized as the potting material has very poorthermal conductive properties, thereby rendering external cooling of theelectron gun extremely difficult.

SUMMARY OF THE PRESENT INVENTION The principal object of the presentinvention is the provision of an electron tube having improved controlgrid cooling.

In one feature of the presentinvention, the electron gun includes anannular cathode-to-anode high voltage insulator body of beryllia ceramicwith the cathode emitter mounted within the central bore of theinsulatorin thermally ins-ulativerelation and with the control gridmounted across the central bore of the insulator in thermally conductiverelation and the insulator body, in turn, mounted in thermallyconductive relation to the body of the electron tube, whereby thecontrol grid is cooled via thermal conduction through the high voltageinsulator to the cooled body of the tube.

In another feature of the present invention, the annular berylliaceramic cathode-to-anode insulator body has an annularly corrugatedsurface facing the anode to define a plurality of radially separatedland portions with the control grid being bonded to-the innermostannular land portion of the insulator body.

In another feature of the present invention, the surface of the annularberyllia ceramic cathode-to-anode insulator includes first and secondannular land portions facing the anode with the control grid affixed tothe first annular land and the focus electrode mounted to the secondland.

Other features and advantages of the present invention will becomeapparentupon a perusal of the following specification taken inconnection with the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS Referring now to FIG. 1 there is shown a microwave highpower klystron tube 1 incorporating features of the present invention.The klystron tube includes an electron gun assembly 2 for forming andprojecting a beam of electrons 3 over an elongated beam path to a beamcollector structure 4 disposed at the terminal end of the elongatedlinear beam 3. A plurality of cavity resonators 5 are successivelyarranged along the beam path for successive electromagnetic interactionwith the electronbeam passable therethrough.

Microwave energy to be amplified is applied to the upstream cavity 5'via an input coupling means, such an input coupling loop 6. Themicrowave energy in the input cavity 5' velocity modulates the beam 3.The velocity modulated beam excites successive floating cavity resonator5 disposed along the beam path to promeans, such asoutput coupling loop7, which couples the energy to a suitable load, such as an antenna, notshown.

A solenoid 8 or permanent magnet structure, schematically represented bysolenoid 8, is disposed around the tube forproducing an axially directedbeam focusing magnetic field throughout the length of the beam path fromthe gun to the collector 4 for focusing the beam through the structuresdisposed along the beam path.

In the electron gun 2, a negative potential, as ofl kV, is applied tothe cathode emitter 10 from a beam power supply 9. The control grid 11overlays the cathode emitter 10 for controlling the beam current. Thecontrol grid 11 is bias negative relative to the cathode 10 by arelatively'small dc bias potential as of a few hundred volts, suppliedby potential supply 12. The control grid 11 is pulsed positive relativeto the cathode 10 for turning on the beam by apulse pwoer supply 13,thereby pulsing the beam current. A relatively small power supply 14, asof 7 volts, is connected across the heater leads of a heating element 15for heating the cathode 10 to thermionic emission temperature, as of 800C.

The body of the tube 1 is preferably operated at ground potential whichis also anode potential Va and is provided with means for cooling thebody of the tube and keeping its temperature at approximately 65 to 76C, in use. In a typical example, the body of the tube 1 is made ofcopper and is cooled by means of fluid coolant passageways (tubes) 16disposed in heat exchanging relation with the body of the tube 1. Fluidcoolant such as water is directed through the coolant tubes 16 forremoving heat from the body of the tube.

Referring now to FIG. 2, there is shown the electron gun assembly 2incorporating features of the present invention. More particularly, thegun includes a centrally apertured anode plate 17 forming a portion ofand operating at the potential of the body of the tube 1, namely groundpotential. The electron gun 2 includes an annular anode-to-cathodeinsulator body 18 of beryllia ceramic. The thermionic cathode emitter 10is mounted within the central bore 19 of the insulator body 18 inthermally insulative relation relative to the insulator body 18.

The insulator body 18 is joined to the anode portion 17 of the body ofthe tube 1 via the intermediary of an annular metallic sealing member21, as of copper. More particularly, sealing member 21 includes arelatively thin wall tubular portion 22, as of 0.025 thick, sealed as bybrazing to the adjacent surface of the insulator 18 at 23 to provide athermally conductive joint at 23 between the sealing member 21 and theinsulator 18. The tubular portion 22 of the sealing member 21 is maderelatively thin to allow for unequal radial thermal expansion betweenthe insulator body 18 and sealing member 21 without producing excessivestrain on the relatively brittle insulator 18. The other end of thesealing member 21 may be brazed to the copper anode 17 to provide a goodthermally conductive joint between the sealing member 21 and the body ofthe tube. As an alternative, the sealing member 21 merely abutts theanode l7 and is sealed to the anode l7 and main body of the tube 1 via apair of radially directed sealing rings 24 and 25 which are brazed attheir inner ends to the sealing member 21 and anode 17, respectively,and are sealed together at theirouter periphery, as by heliarc welding,at 26 to provide a vacuum tight joint between the electron gun -2 andthe anode l7. Atmospheric presusre on the outside of the electron gun -2pushes the sealing member 21 into good thermal contact with the anode17.

The surface of the annular high voltage insulator 18 I which faces theanode 17 is provided with first and second annular grooves 27 and. 28defining first, second and third annular land portions 29, 31 and 32.The control grid 11 includes a multiapertured spherically concavecentral portion 32 and a radially directed outer lip portion 33. The lipportion 33 is brazed at its outer periphery to the top of the first land29 to provide a thermally conductive joint between the control grid 11and the thermally conductive insulator 18.

A beam focus ring 34, as of stainless steel, is disposed intermediatethe control grid 11 and anode 17 for focusing the electron beam througha constricted central aperture 35 of the anode 17. The focus ring 34 ismounted to the second annular land 31 via a sealing ring 36, as ofkovar, and an annular ceramic backup ring 37, as of beryllia ceramic, issealed to the opposite side of the ring 36 from that of the land 31 toequalize the thermal stress on the sealing ring 36. The annular grooves27 and 28 serve to increase the electrical leakage path along thesurface of the insulator 18 to permit high voltages to be appliedbetween electrodes without producing electrical breakdown across thesurface of the insulator 18.

A control grid lead 38 passes through an axially directed bore 39 ininsulator 18 and is connected to the lip 33 of the control grid 11 forapplying the operating potential thereto. Likewise, a focus electrodelead 41 passes axially through a bore 42 in the insulator 18 and isconnected at one end to the focus electrode support ring 36 for applyingthe focus electrode potential to focus-ring 34. In a preferredembodiment, the focus ring 34 is operated at cathode potential and thus,the other end of focus lead 41 is connected to the metallic cathodesupport structure at 43.

The thermionic cathode emitter 10, in a preferred embodiment, comprisesnickel oxide coated cathode consisting of a spherically concave nickelbase member having its concave face preferably dimpled with amultiplicity of spherically concave dimples of lesser radius ofcurvature arranged in a closely packed geometry and coated with acathode emissive material in the conventional manner. The heatingelement 15 is disposed adjacent the backside of the cathode emitterbutton and serves to heat the cathode emitter 10 to operatingtemperature, as of 800 C. The cathode emitter button is carried at itsperiphery in a hollow tubular member 44, as of molybdenum. A pluralityof heat shielding partitions 45 are sealed across the tubular member 44for retaining the heat within the immediate region of the cathodeemitter 10. A second hollow cylindrical heat shield 46 surrounds thecathode emitter support 44 to minimize loss of heat by radiation to thesurrounding ceramic insulator 18. Shield 46 is spaced from the innerwall 19 of the insulator to minimize transfer of thermal energy from thecathode assembly to the surrounding cathode-to-anode insulator 18.

The cathode support tube 44 includes an outwardly flared base portion 47which is sealed as by brazing to an inner mounting ring 48. Mountingring 48 includes a shoulder 49 which abutts a similar mating shoulder onan outer mounting ring 51 which is carried from the high voltageinsulator 18 via the intermediary of a kovar sealing ring 52 brazed tothe outer mounting ring 51 and to the insulator 18 at 53. The matingshoulder on the outer mounting ring 51 is machined accurately withrespect to the top of the land 29 such that when the shoulder 49 of theinner mounting ring 48 is pressed into axial engagement therewith theemitting surface of the cathode emitter is accurately positionedrelative to the position of the control grid 11 which is carried fromthe top of the first land 29. The mounting rings 48 and 51 are laserwelded together at 54 to fixedly secure the cathode and heater assemblywithin the insulator 18.

The electron gun assembly 2 is closed at the bottom end via an endclosing disc 55 as of alumina ceramic, which is mounted to the firstsealing ring 52 via a mating sealing ring 56, as of kovar, brazed to theclosing plate 55. The mating sealing rings 52 and 56 are outtive pottingcompound 63. A suitable potting compound is silicone rubber.

ln a typical example of an X-band multi-cavity kly stron amplifier, theanode-to-cathode insulator 18 has an outer diameter of 2 inches and anaxial length of 0.5 inches. The inside diameter of the central bore 19at its narrowest point is approximately 0.6 inches and the spacingbetween the anode-to-cathode insulator 18 and the anode 17 isapproximately 0.347 inches. The cathode emitter 10 operates atapproximately 800 C and the control grid ll operates at a temperature ofapproximately 200 C at its center and 150 C at its outer periphery,whereas the body of the tube operates at approximately 7 5 to 65 C. Thefocus electrode 34 operates at approximately 100 C. Thus, ample coolingis obtained for the control grid 11 via the thermal conduction achievedthrough the beryllia anode-tocathode insulator l8 and mounting ring 21to the body of the tube 1.

A particular advantage of the anode-to-cathode insulator 18 of FIG. 2 isthat'the surface of the insulator 18 which faces the anode may be groundflat to facilitate obtaining precise positional referencing of thecontrol grid 11 and focus ring 34 relative to the cathode emitter 10 andanode 17.

Referring now to FIG. 3 there is shown an alternative embodiment of thepresent invention. In this embodiment, the annular anode-to-cathodeinsulator body 18 includes an axially directed hollow cylindricalportion 68 which is joined to the body of the tube via a pair ofconcentric annular tubular leg portions 22 of the mounting ring member21. The parallel legs 22 define a fluid coolant passageway 69 in thespace between the legs 22 such that the fluid coolant may be broughtinto direct contact with the end of the insulator 68 to facilitatecooling of the anode-to-cathode insulator 18 and to allow higheranode-to-cathode voltage to be employed due to the increased axiallength of the anodeto-cathode insulator body.

What is claimed is:

1. In an electron tube:

thermionic cathode emitter means having a concave cathode emittingsurface for supplying copious thermionic. electron emission;

centrally apertured anode means axially spaced from said cathode emittermeans and disposed facing said cathode emitter surface for forming andprojecting a beam of electrons over a beam path to a beam collectorstructure; i

focus electrode means disposed surrounding said beam path intermediatesaid cathode emitter and said anode for focusing said beam through saidcentral aperture in said anode means;

control grid means disposed across said beam path between said focuselectrode and said cathode emitter for controlling the beam current;evacuable envelope means for enclosing said beam path, said thermioniccathode emitter means, and said focus electrode meansQsaid envelopemeans including a thermally conductive metallic body portion'enc'losingthe beam path between said anode means and said beam collector, andmeans for cooling said body'portion of said envelope;

high voltage insulator means forming a portion of said evacuableenvelope means and disposed between said cathode emitter means and saidanode means for holding off the beam potential to be applied betweensaid cathode emitter means and said anode means in use, said insulatormeans comprising an annular insulator body of beryllia ceramic, saidcathode'emitter means being mounted substantially within the centralbore in said annular insulator body in thermally insulative relationrelative to the wall of said bore, said control grid means and saidfocus electrode means being mounted at their peripheries to said annularberyllia insulator body; and

mounting means for mounting saidannular beryllia insulator body to saidbody portion of said evacuable envelope in heat exchanging relation withsaid body, whereby said control grid is cooled by thermal conductionthrough said beryllia insulator body to said cooled body portion of thetube;

2. The apparatus of claim 1 wherein said annular insulator body includesan annularly corrugated surface facing said anode means to definefirstand second annular lands separated by a first annular groove, andsaid control grid means and said focus electrode means being mounted tosaid first and second lands, respectively.

3. The apparatus of claim 2 wherein said annular beryllia insulator bodyincludes a second annular groove in said surface facing said anode todefine a third annular'land, and wherein said mounting means formounting said beryllia insulator to said cooled body portion of saidevacuable envelope is bonded to said third annular land.

4. The apparatus of claim 1 wherein said mounting means includes a thinyieldable metallic tubular portion bonded via a gas tight sea] at oneend to said insulator body. 1

5. The apparatus of claim 2 wherein-the top portions of said first andsecond lands of said insulator body lie in substantially the same planewhich is normal to the longitudinal axis of the beam path.

6. The apparatus of claim 3 wherein the top portions of said first,second and third lands of said insulator tion cooling of said gridthrough said beryllia ceramic 8 body.

8. The apparatus of claim 1 including heat shield means interposedbetween said cathode emitter means and the wall of said bore in saidinsulator body for thermally insulating said cathode emitter from saidberyllia insulator.

1. In an electron tube: thermionic cathode emitter means having aconcave cathode emitting surface for supplying copious thermionicelectron emission; centrally apertured anode means axially spaced fromsaid cathode emitter means and disposed facing said cathode emittersurface for forming and projecting a beam of electrons over a beam pathto a beam collector structure; focus electrode means disposedsurrounding said beam path intermediate said cathode emitter and saidanode for focusing said beam through said central aperture in said anodemeans; control grid means disposed across said beam path between saidfocus electrode and said cathode emitter for controlling the beamcurrent; evacuable envelope means for enclosing said beam path, saidthermionic cathode emitter means, and said focus electrode means, saidenvelope means including a thermally conductive metallic body portionenclosing the beam path between said anode means and said beamcollector, and means for cooling said body portion of said envelope;high voltage insulator means forming a portion of said evacuableenvelope means and disposed between said cathode emitter means and saidanode means for holding off the beam potential to be applied betweensaid cathode emitter means and said anode means in use, said insulatormeans comprising an annular insulator body of beryllia ceramic, saidcathode emitter means being mounted substantially within the centralbore in said annular insulator body in thermally insulative relationrelative to the wall of said bore, said control grid means and saidfocus electrode means being mounted at their peripheries to said annularberyllia insulator body; and Mounting means for mounting said annularberyllia insulator body to said body portion of said evacuable envelopein heat exchanging relation with said body, whereby said control grid iscooled by thermal conduction through said beryllia insulator body tosaid cooled body portion of the tube.
 2. The apparatus of claim 1wherein said annular insulator body includes an annularly corrugatedsurface facing said anode means to define first and second annular landsseparated by a first annular groove, and said control grid means andsaid focus electrode means being mounted to said first and second lands,respectively.
 3. The apparatus of claim 2 wherein said annular berylliainsulator body includes a second annular groove in said surface facingsaid anode to define a third annular land, and wherein said mountingmeans for mounting said beryllia insulator to said cooled body portionof said evacuable envelope is bonded to said third annular land.
 4. Theapparatus of claim 1 wherein said mounting means includes a thinyieldable metallic tubular portion bonded via a gas tight seal at oneend to said insulator body.
 5. The apparatus of claim 2 wherein the topportions of said first and second lands of said insulator body lie insubstantially the same plane which is normal to the longitudinal axis ofthe beam path.
 6. The apparatus of claim 3 wherein the top portions ofsaid first, second and third lands of said insulator body liesubstantially in the same plane which is normal to the longitudinal axisof the beam path.
 7. The apparatus of claim 1 wherein said control gridmeans includes a concave grid portion extending across said beam pathand an annular radially directed lip portion, said lip portion beingbonded to said insulator body in heat exchanging relation therewith forconduction cooling of said grid through said beryllia ceramic body. 8.The apparatus of claim 1 including heat shield means interposed betweensaid cathode emitter means and the wall of said bore in said insulatorbody for thermally insulating said cathode emitter from said berylliainsulator.